Active Feedback Analog Filter for Low-Spur RF Frequency Synthesis
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional Direct Digital Sequence (DDS) frequency synthesis techniques face limitations in power consumption, memory requirements, circuit footprint, and high spurious frequency components, which are challenging for high-frequency applications like 5G networking and hand-held communications, especially due to the Nyquist frequency limit and high digital signal processing demands.
Innovation Solution
The implementation of a tunable active feedback circuit with variable resonators and a variable gain block in an analog filter, which narrows the passband to select desired frequency components, allowing for extended frequency range and reduced spurious components, thereby overcoming the limitations of conventional DDS systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional DDS frequency synthesis is used, then frequency tunability is achieved, but power consumption increases significantly
Solution Approach 1:
The patent replaces the conventional digital signal processing system with an analog filter-based system. Specifically, it substitutes the digital frequency synthesis approach with an analog filter that processes the output of a numerically controlled oscillator, thereby reducing the power consumption associated with high-speed digital processing while maintaining frequency tunability through analog filtering mechanisms.
Solution Approach 2:
The patent extracts and removes the high-power digital signal processing components from the frequency synthesis system. By separating the frequency generation function (performed by the NCO) from the frequency selection function (performed by the analog filter), the system eliminates the need for power-intensive digital processing while preserving the desired frequency tunability.
2Adaptability or versatility
If conventional DDS frequency synthesis is used, then frequency synthesis capability is achieved, but spurious frequency components increase
Solution Approach 1:
The patent introduces an analog filter as an intermediary component between the numerically controlled oscillator and the output. This analog filter acts as a mediator that selectively passes the desired frequency component while attenuating spurious frequency components, thereby improving spectral purity without compromising the frequency synthesis capability of the system.
Solution Approach 2:
The patent converts the harmful spurious frequency components into a manageable problem by using the analog filter to selectively suppress them. The filter transforms the broadband output of the NCO, which contains many frequency components, into a clean sinusoidal output by attenuating the unwanted spurious components while preserving the desired frequency.
3Adaptability or versatility
If conventional DDS frequency synthesis is used, then frequency tuning is achieved, but circuit footprint increases
Solution Approach 1:
The patent replaces the large digital signal processing circuitry with a more compact analog filter implementation. By substituting the digital frequency selection mechanism with an analog filter, the system achieves frequency tuning functionality with a significantly reduced circuit footprint, as analog filters generally occupy less area than equivalent digital processing systems.
4Adaptability or versatility
If conventional DDS frequency synthesis is used, then frequency generation is achieved, but memory requirements increase
Solution Approach 1:
The patent extracts and removes the large lookup table memory from the frequency synthesis system. By using an analog filter to perform frequency selection instead of digital processing, the system eliminates the need for extensive memory storage of frequency data, thereby reducing memory requirements while maintaining frequency generation capability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach significantly reduces power consumption, memory requirements, and spurious components, enabling frequencies beyond the synthesizer clock frequency with improved spectral purity and phase coherence, suitable for high-performance RF communications and radar applications.
Implementation Method 1
The analog filter comprises a tunable, active feedback circuit having one or more variable resonators and a variable gain block connected in a signal loop
Data Source
AI summary
A method and apparatus for generating an RF signal uses digital signal components to generate a synthesized RF signal having a plurality of frequency components. An analog filter is used to filter the synthesized RF signal. The analog filter is a tunable, active feedback circuit having one or more variable resonators and a variable gain block connected in a signal loop that is defined by a passband. The analog filter is tuned such that the passband of the analog filter overlaps one or more desired frequency components of the plurality of frequency components of the synthesized RF signal, and such that the passband has a relative bandwidth of about 1% or less.